Recently, a technique of optically forming a three-dimensional object from a photo-curable liquid resin composition on the basis of data output from a three-dimensional CAD system is on widespread use because the desired three-dimensional object can be manufactured at satisfactory dimensional precision without a need for molds or the like. This technique is broadly referred to as rapid prototyping and specifically as stereolithography. With respect to this technique, JP-A 56-144478 (Kodama) disclosed a method of forming a three-dimensional object by supplying a required amount of optical energy to a photo-curable resin, and JP-A 60-247515 established a practically acceptable method. Thereafter, similar or improved techniques were proposed as disclosed in JP-A 62-35966 corresponding to U.S. Pat. Nos. 4,575,330, 4,929,402, 5,174,943, 5,236,637, 5,344,298, 5,554,336, 5,556,590, 5,569,431, 5,571,471, 5,573,722, 5,630,981, 5,762,856, 5,779,967, 5,785,918, 5,814,265 and 6,027,324, JP-A 1-204915, JP-A 2-113925, JP-A 2-145616, JP-A 2-153722, JP-A 3-15520 corresponding to U.S. Pat. No. 4,942,066, JP-A 3-21432 corresponding to U.S. Pat. No. 5,014,207, and JP-A 3-41126 corresponding to U.S. Pat. No. 4,942,060.
A typical method of optically manufacturing a three-dimensional object involves selectively irradiating an ultraviolet laser beam to the surface of liquid photo-curable resin contained in a vat under the control of a computer to harden the photo-curable resin so that a photo-cured resin layer having a predetermined thickness is obtained, then supplying a layer of liquid photo-curable resin onto the cured resin layer and then likewise irradiating an ultraviolet laser beam to the liquid photo-curable resin layer to form a cured resin layer contiguous to the previous one, and repeating the laminating operations until a desired three-dimensional object is obtained. Great attention has recently been paid to this rapid prototyping technique because a three-dimensional object of complex configuration can be formed with ease and within a relatively short time.
To actinic energy radiation-curable resin compositions for use in the rapid prototyping are imposed many requirements including high cure sensitivity to actinic energy radiation, good resolution of a shaped object, high precision of shaping, a minimal volume shrinkage factor upon curing, good mechanical properties of cured product, good self-adherence, good curing properties in an oxygen-containing atmosphere, a low viscosity, resistance to water or moisture, minimal absorption of water or moisture with time, and dimensional stability. Prior art resin compositions known to be used in the rapid prototyping include photo-curable acrylate resin compositions, photo-curable urethane-acrylate resin compositions, photo-curable epoxy resin compositions, photo-curable epoxy-acrylate resin compositions, and photo-curable vinyl ether resin compositions.
There is a need for resins which when processed by the rapid prototyping technique, exhibit “rubber-like property,” that is, the nature that they easily undergo deformation, without rupture, under an applied stress and resume the original shape after the stress is relieved. However, the structures obtained by curing these resins are basically rigid and exhibit the nature that they fail when a stress above a certain level is applied.
There is commercially available only one system, referred to as “elastomer-like,” in which a softener component is admixed with a photo-curable urethane-acrylate resin composition in order for the composition to approach the “rubber-like property” (see JP-A 9-169827). The cured product of this resin exhibits soft properties like ordinary rubber, but non-elastic properties of not resuming the original shape even after stress relief.
A number of materials that exhibit rubber elasticity independently of photo-curing are used in the industry. Typical examples include ethylene-propylene rubber, butadiene rubber, polyurethane rubber, silicone rubber, and fluoro-rubber. However, the resin which cures into a practically acceptable state upon exposure to actinic energy radiation is limited to the silicone rubber. For UV-curable organopolysiloxanes in particular, many examples are disclosed in several patents:
JP-A 6-322272, JP-A 7-216232,
JP-A 11-12556 corresponding to U.S. Pat. No. 6,013,693,
JP-A 11-60953, JP-A 11-228702,
JP-A 2002-371261, JP-A 2003-213132, JP-A 8-059843,
JP-A 8-231732 corresponding to U.S. Pat. No. 5,877,228
JP-A 5-222143,
JP-A 7-228780 corresponding to U.S. Pat. No. 5,591,783.
Although the compositions described in these patents cure upon exposure to actinic energy radiation, their cure rate is yet too slow to apply to the stereolithography so that they could not be used in practical rapid prototyping. Even when they are cured to completion with the time taken therefor being neglected, the resulting rubber model will become embrittled shortly and exhibit no longer rubber elasticity. It would be desirable to have a resin which is amenable to the rapid prototyping or stereolithography and exhibits and maintain rubber elasticity.